It is desirable in many polymerization processes, particularly a slurry phase or gas phase process, to use a supported catalyst. Generally these catalyst systems include a metallocene and alumoxane supported on the same carrier, such as silica, and subsequently dried to a powder. For example, U.S. Pat. No. 4,937,217 generally describes a mixture of trimethylaluminum and triethylaluminum added to an undehydrated silica then adding a metallocene to form a dry catalyst. EP-308177-B1 generally describes adding a wet monomer to a reactor containing a metallocene, trialkylaluminum and undehydrated silica. U.S. Pat. Nos. 4,912,075, 4,935,397 and 4,937,301 generally relate to adding trimethylaluminum to an undehydrated silica and then adding a metallocene to form a dry supported catalyst. U.S. Pat. No. 4,914,253 describes adding trimethylaluminum to undehydrated silica, adding a metallocene and then drying the catalyst with an amount of hydrogen to produce a polyethylene wax. U.S. Pat. Nos. 4,808,561, 4,897,455 and 4,701,432 describe techniques to form a supported catalyst where the inert carrier, typically silica, is calcined and contacted with a metallocene(s) and a activator/cocatalyst component. U.S. Pat. No. 5,238,892 describes forming a dry supported catalyst by mixing a metallocene with an alkyl aluminum then adding undehydrated silica. U.S. Pat. No. 5,240,894 generally pertains to forming a supported metallocene/alumoxane catalyst system by forming a metallocene/alumoxane reaction solution, adding a porous carrier, evaporating the resulting slurry to remove residual solvent from the carrier.
There are also those U.S. Pat. Nos. 5,008,228, 5,086,025 and 5,147,949 which generally describe forming a dry supported catalyst by the addition of trimethylaluminum to a water impregnated silica to form alumoxane in situ the silica pores and then adding the metallocene. While these supported catalysts are useful it would be desirable to have an improved catalyst system to produce polymers that are easier to process and produce. Particularly in a slurry or gas phase polymerization process, using these catalysts systems, there is a tendency for reactor fouling during polymerization within the reactor. During a typical polymerization process fines within the reactor often accumulate and cling or stick to the wails of a reactor. This phenomenon is often referred to as "sheeting". The accumulation of polymer particles on the reactor walls, the recycling lines and cooling system results in many problems including poor heat transfer in the polymerization process. Polymer particles that adhere to the walls of the reactor continue to polymerize and often fuse together and form chunks, which can be detrimental to a continuous process.
It would be highly desirable to have an improved polymerization catalyst that in a polymerization process would significantly enhance reactor operability and provide an improved polymer product.